Ah, just done a bit of checking. I had assumed that the gshield was some kind of stepper driver interface. I now see that is a stepper driver card, aimed at lower voltage/power steppers than something like the AM882.

I'm not sure if your gshield is working, once the pins were straightened. If you have one of those in working order, then do you really need a whole new controller plus stepper drivers? Could you not use a cheap Arduino board to run grbl, and connect it to the gshield? I think grbl runs OK on an Arduino Uno, about £20 from Amazon. You would end up with something that's pretty well equivalent to the CNC xPRO, as far as I can see.